Systems and methods for filtering radio frequencies from a signal of a thermocouple and controlling a temperature of an electrode in a plasma chamber

ABSTRACT

A method includes: receiving a first signal from a first sensor at a first filter and preventing passage of a first portion of the first signal via the first filter. The first portion of the first signal is at a first RF. A second portion of the first signal is indicative of a first temperature of a first electrode in a plasma chamber. The method further includes: outputting a second signal from the first filter; receiving the second signal at a second filter; and preventing passage of a portion of the second signal via the second filter. The portion of the second signal is at a second RF. The second RF is less than the first RF. The first filter and the second filter are implemented on a printed circuit board. The method further includes adjusting a temperature of the first electrode based on an output of the second filter.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present disclosure is a continuation of U.S. patent application Ser.No. 14/965,030 filed on Dec. 10, 2015. This application claims thebenefit of U.S. Provisional Application No. 62/247,979 filed on Oct. 29,2015. The entire disclosures of the applications referenced above areincorporated herein by reference.

FIELD

The present disclosure relates to substrate processing systems, and moreparticularly to systems and methods for controlling temperatures of anelectrode in a substrate processing system.

BACKGROUND

The background description provided here is for the purpose of generallypresenting the context of the disclosure. Work of the presently namedinventors, to the extent it is described in this background section, aswell as aspects of the description that may not otherwise qualify asprior art at the time of filing, are neither expressly nor impliedlyadmitted as prior art against the present disclosure.

Substrate processing systems may be used to perform etching, deposition,and/or other treatment of substrates such as semiconductor wafers.Example processes include, but are not limited to, chemical vapordeposition (CVD), atomic layer deposition (ALD), and/or other etch,deposition, and cleaning processes. A substrate may be arranged on asubstrate support such as a pedestal, an electrostatic chuck (ESC), etc.in a processing chamber of the substrate processing system. Differentgas mixtures including one or more precursors may be introduced into theprocessing chamber and plasma may be used to actuate chemical reactions.

During processing of a substrate, temperatures of the substrate andcomponents of the substrate processing system may vary. Thesetemperature variations may have undesirable effects on the resultingsubstrates. Accordingly, the substrate processing systems may implementsystems and methods for controlling temperatures of the substrate andcomponents of the substrate processing system.

SUMMARY

A circuit is provided and includes a first filter assembly and acontroller. The first filter assembly is implemented on a printedcircuit board. The first filter assembly includes a first filter and asecond filter. The first filter is configured to (i) receive a firstsignal from a first sensor, (ii) prevent passage of a first portion ofthe first signal, and (iii) output a second signal. The first portion ofthe first signal is at a first radio frequency. A second portion of thefirst signal is indicative of a first temperature of a first electrodein a plasma chamber. A second filter is configured to (i) receive thesecond signal, and (ii) prevent passage of a portion of the secondsignal. The portion of the second signal is at a second radio frequency.The second radio frequency is less than the first radio frequency. Thecontroller is configured to adjust a temperature of the first electrodebased on an output of the second filter.

In other features, a circuit is provided and includes a first filterassembly and a controller. The first filter assembly includes a bandstop filter and a low pass filter. The band stop filter is configured to(i) receive a first signal from a first sensor, (ii) prevent passage ofa first portion of the first signal, and (iii) and output a secondsignal. The first portion of the first signal is at a first radiofrequency. A second portion of the first signal is indicative of a firsttemperature of a first electrode in a plasma chamber. The low passfilter is configured to (i) receive the second signal, and (ii) preventpassage of a portion of the second signal. The portion of the secondsignal is at a second radio frequency. The second radio frequency isless than the first radio frequency. The controller is configured toadjust a temperature of the first electrode based on an output of thelow pass filter.

In other features, a method is provided and includes: receiving a firstsignal from a first sensor at a first filter; preventing passage of afirst portion of the first signal via the first filter, where the firstportion of the first signal is at a first radio frequency, and where asecond portion of the first signal is indicative of a first temperatureof a first electrode in a plasma chamber; outputting a second signalfrom the first filter; and receiving the second signal at a secondfilter. The method further includes: preventing passage of a portion ofthe second signal via the second filter, where the portion of the secondsignal is at a second radio frequency, where the second radio frequencyis less than the first radio frequency, and where the first filter andthe second filter are implemented on a printed circuit board; andadjusting a temperature of the first electrode based on an output of thesecond filter.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description, the claims and the drawings. Thedetailed description and specific examples are intended for purposes ofillustration only and are not intended to limit the scope of thedisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of an example of a substrateprocessing system incorporating filter assemblies according to thepresent disclosure;

FIG. 2 is a functional block diagram of an example of a temperaturecontrol system for electrodes of multiple stations according to thepresent disclosure;

FIG. 3 is a functional block diagram of an example of a temperaturecontrol system for a single electrode according to the presentdisclosure;

FIG. 4 is a functional block diagram of an example of a temperaturecontrol system for a single electrode illustrating closed looptemperature control of a filter assembly according to the presentdisclosure;

FIG. 5 a functional block diagram of another example of a temperaturecontrol system for a single electrode illustrating closed looptemperature control of a filter assembly according to the presentdisclosure;

FIG. 6 is example of an equivalent circuit representation for a filterassembly and an isolation device of a thermocouple according to thepresent disclosure;

FIG. 7 is a functional block diagram and schematic of an example of afilter assembly according to the present disclosure;

FIG. 8 is a side view of an example of a core-based filter assemblyaccording to the present disclosure;

FIG. 9 illustrates an example of a temperature control method accordingto the present disclosure;

FIG. 10 is a plot illustrating examples of station temperatures withtraditional filtering; and

FIG. 11 is a plot illustrating examples of station temperatures withfiltering according to the present disclosure.

In the drawings, reference numbers may be reused to identify similarand/or identical elements.

DETAILED DESCRIPTION

In an effort to improve particle performance and throughput in a plasmachamber, a temperature of a showerhead is maintained at a predeterminedtemperature during substrate processing. The showerhead may includeembedded heaters to heat the showerhead and a thermocouple to sense atemperature of the showerhead. The improved temperature control allowsfor increased accumulation levels while meeting particle requirements.As a result, a greater number of wafers may be processed betweencleaning events, which improves productivity.

Intermittent coupling of DC may occur from the showerhead to conductorsof the thermocouple. DC is caused by a high RF potential, which causes a“diode effect” or a nonlinear electrical response resulting in asymmetrybetween positive and negative halves of an electrical cycle. DC can alsobe supplied from a DC voltage supply source and is referred to as “aparticle repulsion field (PRF)”. The PRF charges the showerhead with aDC voltage to electrostatically mitigate particles shortly after thehigh RF potential is switched OFF.

Although the thermocouple may be insulated from the substrate processingchamber and the showerhead, DC begins to appear on the thermocouple asinsulation of the thermocouple degrades. Degradation of the insulationcauses DC leakage and/or coupling between the thermocouple and theshowerhead. Additionally, RF signals supplied to the showerhead canstrongly couple to the thermocouple embedded in the showerhead. Whilethe RF signals of a station may be isolated before reaching itscorresponding temperature controller, the RF signals can couple to othernearby stations or to a ground reference, which may cause RF imbalance,arcing, and RF noise. The RF power may be different from one station toanother which causes different levels of DC coupling.

Temperature measurements output by the thermocouple are relatively smallDC voltages. These temperature measurements are overcome by DC couplingsignals when DC coupling occurs. Temperature control systems and methodsaccording to the present disclosure include filter circuits andassemblies that substantially reduce the effects of DC coupling.

Referring now to FIG. 1, a substrate processing system 100 forperforming etching using RF plasma is shown. While a PECVD chamber isshown, the systems and methods described herein may be used in otherprocesses. The substrate processing system 100 includes an RF enclosure101 that may be at atmospheric pressure or another pressure. Aprocessing chamber 102 is located in the RF enclosure 101. Theprocessing chamber 102 encloses other components of the processingchamber 102 and contains the RF plasma. The processing chamber 102includes an upper electrode 104 and a substrate support 106. Duringoperation, a substrate 108 is arranged on the substrate support 106.

For example only, the upper electrode 104 may be a showerhead 109 thatdistributes gases. The upper electrode 104 may include a stem portion111 including one end connected to a top surface of the processingchamber 102. A base portion of the showerhead 109 is generallycylindrical and extends radially outwardly from an opposite end of thestem portion 111 at a location that is spaced from the top surface ofthe processing chamber 102. A substrate-facing surface of the showerhead109 includes a plate with holes through which process or purge gasflows. The showerhead 109 includes heating elements 113. The showerhead109 may also include cooling channels (not shown) that flow cooling gasor fluid. Examples of a showerhead 109 having cooling channels is shownand described in U.S. application Ser. No. 13/900,627, filed on May 23,2013 and titled “RF-Powered, Temperature-Controlled Gas Diffuser”, whichis incorporated herein by reference in its entirety.

The substrate support 106 includes a conductive baseplate 110 that actsas a lower electrode. The baseplate 110 supports a heating plate 112,which may be formed at least partially of a ceramic material. A thermalresistance layer 114 may be arranged between the heating plate 112 andthe baseplate 110. The baseplate 110 may include one or more channels116 for flowing coolant through the baseplate 110.

A RF generating system 120 generates and outputs RF power to the upperelectrode 104. The baseplate 110 may be DC grounded, AC grounded or at afloating potential. For example only, the RF generating system 120 mayinclude an RF generator 122 that generates the RF power, which is fed bya matching and distribution network 124 to the upper electrode 104. Inone embodiment, RF power is provided at two or more frequencies to theupper electrode 104. For example only, RF power is supplied at a firstfrequency (e.g., 13.56 mega-hertz (MHz)) and RF power is also suppliedat a second frequency (e.g., 400 kilo-hertz (kHz)). The first frequencymay be higher than an ion cut-off frequency to excite electrons and notions in a plasma. The second frequency may be less than the ion cut-offfrequency to excite both ions and electrons in the plasma.

A gas delivery system 130 includes one or more gas sources 132-1, 132-2,. . . , and 132-N (collectively gas sources 132), where N is an integergreater than zero. The gas sources 132 supply one or more precursors andmixtures thereof. The gas sources 132 may also supply purge gas.Vaporized precursor may also be used. The gas sources 132 are connectedby valves 134-1, 134-2, . . . , and 134-N (collectively valves 134) andmass flow controllers 136-1, 136-2, . . . , and 136-N (collectively massflow controllers 136) to a manifold 140. An output of the manifold 140is fed to the showerhead 109.

A temperature controller 142 may be connected to temperature controlledelements (TCEs) 144 arranged in the heating plate 112. Although shownseparately from a system controller 160, the temperature controller maybe implemented as part of the system controller 160. The temperaturecontroller 142 may control the temperatures of the heating elements 113and the TCEs 144 to control temperatures of the upper electrode 104 andthe substrate support 106, respectively. The temperature controller 142may communicate with a coolant assembly 146 to control coolant throughthe channels 116 of the baseplate 110. For example, the coolant assembly146 may include a coolant pump, a reservoir and flow control devicessuch as valves and/or mass flow controllers.

A valve 150 and pump 152 may be used to control pressure in theprocessing chamber 102 and to selectively evacuate reactants from theprocessing chamber 102. The system controller 160 may control componentsof the substrate processing system 100.

The upper electrode 104 includes one or more thermocouples (onethermocouple 180 having conductors 182 is shown). The thermocouple 180extends through the stem 111 and into the showerhead 109. The stem 111is sealed to the plasma chamber 102 via a seal 184. The conductors 182are received at a first filter assembly 186, which may include a printedcircuit board assembly (PCBA). The output of the first filter assembly186 may be provided to a second filter assembly 188. The second filterassembly 188 may be located within the RF enclosure 101 or may beexternal to the RF enclosure 101, as shown. Examples of the filterassemblies are shown in FIGS. 2-8.

The first filter assembly 186 and optionally the second filter assembly188 may be located in the RF enclosure 101. The first filter assembly186 is located in close proximity to the thermocouple 180 and upperelectrode 104 to minimize and block radio frequencies on the conductors182 and other conductors. Examples of the other conductors include (i)conductors between the first filter assembly 186 and the second filterassembly 188, and/or (ii) conductors between (a) the second filterassembly 188 and (b) temperature controller 142 or an isolation device(shown in FIGS. 2-5)). The first filter assembly 186 may be connected tothe stem 111 and/or to the plasma chamber 102 near the stem 111. Theclose proximity of the first filter assembly 186 to the thermocouple180, stem 111, and/or the upper electrode 104 minimizes RF and/or DCanomalies.

One or more fans 190 may be arranged in the RF enclosure 101 and used tomaintain temperatures within the RF enclosure 101 at a predeterminedtemperature (e.g., 70° C.). This may aid in maintaining temperatures ofthe first filter assembly 186 and/or the second filter assembly 188 atthe predetermined temperature. The fans 190 may be turned ON and OFF bythe temperature controller 142. The temperature controller 142 maycontrol and adjust a duty cycle of control signals provided to each ofthe fans. The duty cycles may be adjusted based on temperatures detectedin the RF enclosure 101, on the first filter assembly 186, and/or viathe thermocouple 180. For example, an ON time per cycle of a controlsignal of a fan may be increased when a detected temperature increasesto provide additional cooling. One or more of the fans 190 may bededicated to controlling a temperature of the first filter assembly 186.This allows for convective cooling of components on the first filterassembly 186. Temperature differences across the first filter assembly186 may be minimized by maintaining the components on the first filterassembly 186 at a same predetermined temperature (e.g., 70° C.). Thisprevents introduction of DC due to temperature differences across a PCBof the first filter assembly 186, as will be described further below.The fans 190 may be located anywhere in the RF enclosure 101.

FIG. 2 shows a temperature control system 200 for electrodes 202 ofmultiple stations. In some examples, the stations may be arranged on acarousel in the plasma chamber 102 of FIG. 1. The electrodes 202 includethe upper electrode 104 of FIG. 1 and receive RF signals as describedabove. Gas may be provided to the electrodes 202 for plasma processing.The electrodes 202 have respective first filter assemblies 204, secondfilter assemblies 206, and isolation devices 208. The first filterassemblies 204 are connected to thermocouples (e.g., an example of whichis shown by the thermocouple 180 of FIG. 1) in the electrodes 202.Outputs of the thermocouples 180 are connected to the first filterassemblies 204. Outputs of the first filter assemblies 204 are connectedto the second filter assemblies 206. Outputs of the second filterassemblies 206 are connected to the isolation devices 208. Outputs ofthe isolation devices 208 are connected to the temperature controller142, which controls current supplied to heating elements in theelectrodes 202 based on temperatures detected via the thermocouples. Inone embodiment, the second filter assemblies 206 are not included andthe outputs of the first filter assemblies are provided directly to theisolation devices 208.

The first filter assemblies, as further described below, include afilter for each conductor of each of the thermocouples. Eachthermocouple may include multiple conductors. Each filter assembly mayinclude a band stop filter and a low pass filter connected in series asfurther described below with respect to FIGS. 7 and 9. The second filterassemblies may include low pass filters respectively for the conductorsof the thermocouples as further described below with respect to FIG. 8.

The isolation devices 208 may be separate from the temperaturecontroller 142 or may be integrated as part of the temperaturecontroller 142. The isolation devices 208 may include amplifiers and/orisolation elements for decoupling low voltage differential signalsreceived from the thermocouple conductors from self-biased DC voltagesof plasma. The isolation devices 208 may amplify condition receivedsignals and remove residual DC interference. Each of the isolationdevices 208 measures a received voltage, compares the received voltageto a non-linear thermocouple curve, calculates an internal temperatureof the isolation device based on the received signal and the non-linearthermocouple curve and encodes the temperature into a linear analogvoltage which it outputs. The self-biased DC voltages can couple intoembedded thermocouple lines in a showerhead. High RF voltage potentials,such as that provided to a showerhead, can erode thermocouple electricalisolation. This can cause an inaccurate DC voltage reading and impropercontrol of heating elements within the showerhead. The isolation devices208 block the DC associated with the plasma and other DC voltages (e.g.,a PRF voltage) and allow for accurate thermocouple DC voltage readingsfor accurate heater element control. The other DC voltages may berelative to a chassis ground.

FIG. 3 shows a temperature control system 230 for a single electrode232, which may replace the upper electrode 104 or any of the electrodes202 of FIGS. 1-2. The temperature control system 230 includes thetemperature controller 142, a filter circuit 233, and a switch 234 andmay include an AC source 236. The filter circuit 233 includes a firstfilter assembly 238, a second filter assembly 240, and an isolationdevice 242. Although the isolation device 242 is shown as being separatefrom the temperature controller 142, the isolation device 242 and thetemperature controller 142 may be implemented as a single device. Thefirst filter assembly 238 may include a PCB and multiple filters foreach conductor of a thermocouple in the electrode 232. The filter foreach conductor of the thermocouple includes a band stop filter and a lowpass filter.

The thermocouple may include multiple pairs of conductors, where eachpair of conductors effectively operates as a respective thermocouple.The second filter assembly 240 may include a thermocouple (TC) filter244 and an over temperature (OT) filter 246, which may be connected toan over temperature monitor. Outputs of the first filter assembly 238associated with a first pair of conductors may be connected to thethermocouple filter 244. Outputs of the first filter assembly 238associated with a second pair of conductors may be connected to the overcurrent filter 246. The filters 244, 246 may be low pass filters and mayinclude wrapping thermocouple conductors around respective iron cores,examples of which are shown in FIG. 8.

The temperature controller 142 may include solid-state relays 250, ashowerhead controller 252 and a limit controller 254. The solid-staterelays 250 may receive RF power from the AC source 236 via the switch234. The switch 234 may be referred to as a safety contactor. The ACpower may be provided via an AC filter 256 to the electrode 232. Thelimit controller 254 may control operation of the switch 234 based onfirst outputs of the isolation device 242 corresponding to outputs ofthe over current filter 246. The showerhead controller 252 controlsoperation of the solid-state relays 250 based on second outputs of theisolation device 242 corresponding to outputs of the thermocouple filter244. The solid-state relays 250 may be controlled to supply RF power tothe electrode 232. The AC filter 256 may include bandpass and/or highpass filters to permit passage of RF signals at predeterminedfrequencies and to prevent passage of DC and/or noise.

Temperature of the first filter assembly 238 may be maintained usingopen loop control or closed loop control. In one embodiment, the firstfilter assembly 238 is temperature regulated and/or cooled viaconductive cooling. This may include a fan circulating or passing airacross the first filter assembly 238 as similarly described above withrespect to the fans 190 of FIG. 1. Examples of closed loop control aredescribed below with respect to FIGS. 4-5.

FIG. 4 shows a temperature control system 270 for the electrode 232. Thetemperature control system 270 includes a temperature controller 272, afirst filter assembly 274, the second filter assembly 240, and theisolation device 242 and may include the switch 234 and the AC source236. The temperature controller 272 includes the solid-state relays 250,the showerhead controller 252 and the limit controller 254. The secondfilter assembly 240 includes the thermocouple filter 244 and the overcurrent filter 246. The temperature controller 272 also includes afilter controller 276, which performs closed loop temperature control ofthe first filter assembly 274.

The first filter assembly 274 may include temperature sensors 280 andone or more cooling devices 282. The temperature sensors 280 may beconnected to a PCB of the first filter assembly 274 near thermocouplesignal inputs and outputs of the PCB. Temperature signals generated bythe temperature sensors 280 are provided to the filter controller, whichregulates temperatures of the first filter assembly 274 to be at a sametemperature. The cooling devices 282 may include air or fluid coolingdevices, such as one or more fans, valves, switches, pumps, etc. Oneexample embodiment of the cooling devices 282 is shown in FIG. 5. Thefilter controller 276 controls operation of the cooling devices 282 toadjust temperatures of the first filter assembly 274. The filtercontroller 276 may control temperatures of one or more filter assembliesof one or more stations. The filter controller 276 may communicate witha controller on the PCB of the first filter assembly 274 or may beincluded on a PCB of the first filter assembly 274. An example PCB ofthe first filter assembly 274 is shown in FIG. 7.

FIG. 5 shows another temperature control system 290 for the electrode232. The temperature control system 290 includes a temperaturecontroller 292, the first filter assembly 274, the second filterassembly 240, and the isolation device 242 and may include the switch234 and the AC source 236. The temperature controller 292 includes thesolid-state relays 250, the showerhead controller 252 and the limitcontroller 254. The second filter assembly 240 includes the thermocouplefilter 244 and the over current filter 246. The temperature controller292 also includes a filter controller 294, which performs closed looptemperature control of the first filter assembly 274.

The first filter assembly 274 may include the temperature sensors 280and one or more cooling devices or other temperature adjusting devices(e.g., heaters). The cooling devices may include a cooling block 296,valves 298, a pump 300 and a coolant reservoir 302. The cooling block296 may be in close proximity of, thermally connected to, directlyconnected to and/or indirectly connected to the first filter assembly274 and/or a PCB of the first filter assembly 274. The temperaturesensors 280 may be connected to the PCB of the first filter assembly 274near thermocouple signal inputs and outputs of the PCB. Temperaturesignals generated by the temperature sensors 280 are provided to thefilter controller 294, which regulates temperatures of the first filterassembly 274 to be at a same temperature. The filter controller 294controls operation of the valves 298, pump 300, and/or other temperatureadjusting devices to adjust flow of a coolant to and from channels 306of the cooling block 296 to adjust temperatures of the first filterassembly 274. This may include zoned cooling including, for example,operating the valves 298 to independently control fluid flow ratesand/or pressures in the channels 306. This allows different zones of thePCB to receive different amounts of cooling. The filter controller 294may control temperatures of one or more filter assemblies respectivelyof one or more stations, where each of the stations has a cooling blockand corresponding first filter assembly. The filter controller 294 maycommunicate with a controller on the PCB of the first filter assembly274 or may be included on the PCB of the first filter assembly 274. Anexample PCB of the first filter assembly 274 is shown in FIG. 7.

FIG. 6 shows an equivalent circuit representation 310 for a filterassembly 312 and an isolation device 314 of a thermocouple. Thisequivalent circuit representation 310 may represent portions of thefirst filter assemblies and isolation devices of FIGS. 1-5 associatedwith a single pair of conductors of a thermocouple and does notrepresent a second filter assembly (e.g., one of the second filterassemblies 188, 206, 240 of FIGS. 1-5). The first filter assembly 312includes a PCB 316, input terminals 318, and output terminals 320. Theisolation device 314 includes a connector 313 with terminals 322 and asignal conditioning circuit 324 having as an input, a thermocouplevoltage VTC, and an output voltage V_(OUT).

Pairs of thermocouple conductors 330, 332 are shown (i) between thethermocouple and the first filter assembly 312, and (ii) between thefirst filter assembly 312 and the connector 313 of the isolation device314. The thermocouple conductors 330, 332 are connected to correspondingones of the terminals 318, 320, 322. Pairs of PCB conductors orintegrated circuit (IC) conductors (e.g., copper traces) 334, 336 areshown (i) between the first pair of thermocouple conductors 330 and thesecond pair of thermocouple conductors 332, and (ii) between the secondpair of thermocouple conductors 332 and the input of the signalconditioning circuit 324. The isolation device 314 and/or the signalconditioning circuit 324 performs an analog-to-digital-to-analogconversion to provide a digitally scaled analog output (the outputvoltage V_(OUT)). The signal conditioning circuit 324 measures athermocouple open circuit voltage VTC with a high impedance circuit tominimize loop current.

Each of the pairs of thermocouple conductors 330, 332 has conductorsmade of different materials, such that conductors of each of the pairsof thermocouple conductors 330, 332 has a respective Seebeck coefficientSa or Sc, as shown. In addition, the conductors 334, 336 have acorresponding Seebeck coefficient Sz. The Seebeck coefficient Sa may befor conductors that include nickel and aluminum. The Seebeck coefficientSc may be for conductors that include nickel and chromium. The Seebeckcoefficient Sz may be for conductors that include copper. TemperaturesTx, T1, T2, Tc and Tv are shown for the temperatures respectively at (i)the output of the thermocouple, (ii) the terminals 318, (iii) theterminals 320, (iv) the terminals 322, and (v) a point on or an outputof the signal conditioning circuit 324.

According to Kirchoff's voltage law, a sum of all voltages around aclosed loop is zero. Thus, the sum of the voltages around the loop ofthe equivalent circuit representation 310 is as shown by equation 1.Rearranging and simplifying equation 1 provides equation 2.Sc(tx−T1)+Sz(T1−t2)+Sc(T2−Tc)+Sz(Tc−Tv)+VTC+Sz(Tv−Tc)+Sa(Tc−T2)+Sz(T2−T1)+Sa(T1−Tx)=0  (1)(Sa−Sc)(T2−T1+Tx−Tc)=VTC  (2)

The values of Sa and Sc determine polarity of VTC. If T2 is equal to T1,then the magnitude of VTC is based on the difference between Tx and Tc,where Tx is the unknown temperature detected by the thermocouple and Tcis a temperature of the connector 313. If T2 is not equal to T1, thenthe magnitude of the voltage VTC is also based on the difference betweenT2 and T1. For this reason and as disclosed herein, temperatures of T2and T1 are maintained at a same temperature. Sensors may be used todetect the temperatures T2 and T1. Example sensors are shown in FIG. 7.The filter controllers 276, 294 of FIGS. 4, 5 may maintain thetemperatures T2 and T1 at the same temperature. In one embodiment, thetemperatures are maintained at a fixed temperature without detecting thetemperatures T2, T1 (referred to as open loop control). For example, thetemperature controller 142 of FIG. 1 may control operation of the fans190 based on a current recipe and predetermined estimates of thetemperatures T2 and T1 for various times during a process. Thetemperature controller 142 may store and/or have access to a table ofestimates of T2 and T1 for different operating conditions and timesduring a process being performed. The temperature controller 142 mayadjust current, voltage, power, frequency, and/or duty cycle of one ormore of the fans 190. Closed loop control may also include controllingcurrent, voltage, power, frequency, and/or duty cycle of one or more ofthe fans 190 based on measurements of T2 and T1. Closed loop control maycontrol open and closed states of valves, ON and OFF states of pumps,speeds of pumps, how much valves are open, frequency of valve openings,etc.

The first filtering assemblies disclosed herein are implemented on PCBAsand provide RF filtering with compact and repeatable designs for ease ofmanufacturing. A thermocouple conductor when interfacing with a coppertrace of a PCB can generate a small voltage due to a thermoelectriceffect (referred to as a Seebeck effect), which can affect a temperaturemeasurement. To prevent this small voltage from being generated, thePCBAs are mounted in an RF enclosure, which is maintained at apredetermined or ambient temperature (e.g., 70° C.). A correspondingtemperature controller may be exposed to the predetermined or ambienttemperature. The PCBAs may be temperature controlled to prevent anytemperature gradients from arising. This is because a Seebeck effect isprimarily affected at dissimilar metal junctions. Althoughthermoelectric voltages can arise, consistent with Kirchoff's voltagelaw, the effects of the dissimilar metal junctions disclosed hereinalong with temperature control of the PCBAs cause the junctions tonullify each other leaving only an originally detected thermocouplevoltage. In contrast, traditional techniques for mitigating DC voltagesuse differential amplifiers, which (i) have a small range of DC voltagesthat can be isolated, and (ii) exhibit finite common mode rejection,resulting in larger errors when a high DC noise to signal ratio exists.

FIG. 7 shows an example of the first filter assembly 350, which may be aPCBA, having a PCB 351. The first filter assembly 350 includes firstfilters 352, second filters 354, a first temperature sensor 356, asecond temperature sensor 358, and a power controller 360. The firstfilters 352 include a first filter 362 (shown as a band stop filter) anda second filter 364 (shown as a low pass filter). The second filters 354include a first filter 366 (shown as a band stop filter) and a secondfilter 368 (shown as a low pass filter). The first filters 362, 366prevent passage of RF power at frequencies within a first frequencyband, which may be centered at or near a first frequency (e.g., 13.56MHz). RF power at the first frequency may be supplied to a showerheadand be detected by a thermocouple. The first filters 362, 366 permitpassage of RF power at frequencies outside of the first frequency band.The second filters 364, 368 prevent passage of RF power at frequenciesabove a cut-off frequency (e.g., 100 kHz) and permit passage of RF powerat frequencies below the cut-off frequency. The frequencies above thecut-off frequency may be referred to as a second frequency band.Frequencies below the cut-off frequency may be referred to as a thirdfrequency band. As a result, RF power at a second frequency (e.g., 400kHz), supplied to the showerhead and detected by the thermocouple, maybe blocked by the second filters 364, 368. RF power at the first RFfrequency and the second RF frequency may be provided to an electrode ina plasma chamber, as described above.

The filters 362, 366 include corresponding inductances 370, 372, 374,375, 376, 377 and capacitances 378, 380. The filters 364, 368 includerespective inductances 382, 384 and capacitances 386, 388. Theinductances 370, 374, 375 are connected in series between input terminal390 and the inductance 382. The inductances 372, 376, 377 are connectedin series between input terminal 392 and the inductance 394. In oneembodiment, values of each of the inductances 370 and 372 are less thanvalues of each of the inductances 374, 375, 376, 377. The values of theinductances 374, 375, 376, 377 may be the same. The input terminals 390,392 may be connected to conductors of the thermocouple. The inductances382, 384 are connected to output terminals 394, 396. The inductances370, 372 are connected in parallel with the capacitances 378, 380. Thecapacitances 386, 388 are connected between outputs of the inductances382, 384 and a ground reference 398.

The temperature sensors 356, 358 are shown as examples. For examplepurposes only, the temperature sensors 356, 358 may include firsttransistors and second transistors. The first transistors may betransitioned between states to supply current to the second transistors.This may turn ON the temperature sensors 356, 358. The temperaturesensors 356, 358 and/or the second transistors may be configured todetect temperatures of and/or near the input terminals 390, 392 and theoutput terminals 294, 296. The temperature sensors 356, 358 may be incontact with the terminals 390, 392, 394, 396. Although two temperaturesensors are shown any number of temperatures sensors may be included. Asanother example, a temperature sensor may be provided for each of theterminals 390, 392, 394, 396.

The temperature sensors 356, 358 may be connected to and receive currentfrom the power controller 360. The temperature sensors 356, 358 may beconnected to and receive control signals from a filter assemblycontroller 410 or one of the filter controllers of FIGS. 4, 5. Outputsof the temperature sensors 356, 358 may be may be connected toanalog-to-digital (ND) converters. Outputs of the A/D converters may beprovided to the filter assembly controller 410 or one of the filtercontrollers of FIGS. 4 and 5. The A/D converters may be included in thefilter assembly controller 410.

As an example, the first transistors of the temperature sensors 356, 358may be metal-oxide-semiconductor field-effect transistors (MOSFETs) andinclude drains, gates and sources. The second transistors of thetemperature sensors 356, 358 may be bipolar junction transistors (BJTs)and include collectors, bases and emitters. The drains may be connectedto and receive current from the power controller 360. The gates may beconnected to and receive control signals from a filter assemblycontroller 410 or one of the filter controllers of FIGS. 4, 5. Thesources of the first transistors may be connected to the collectors andthe bases. The collectors may be connected to the ground reference 398.The collectors and the emitters may be connected to the A/D converters.Outputs of the A/D converters may be provided to the filter assemblycontroller 410 or one of the filter controllers of FIGS. 4 and 5.

The second transistors may be connected in diode configurations.Temperature dependence of base-to-emitter voltages of the secondtransistors may be the basis for temperature measurements. Thebase-to-emitter voltages Vbes may be dependent on temperatures while (i)a power source 416 supplies power via the power module 360 with aconstant level of current to the collectors via the first transistors,and (ii) a voltage across the bases and the collectors is zero. Thevoltages across the bases (or collectors) and the emitters of the secondtransistors may be detected by the A/D converters and/or the filterassembly controller 410. The detected voltages may be converted totemperatures via the filter assembly controller 410 or one of the filterassembly controllers of FIGS. 4 and 5. The filter assembly controller410 or one of the filter assembly controllers of FIGS. 4 and 5 mayreceive digital signals from the A/D converters and determine thetemperatures of the terminals 390, 392, 394, 396 (e.g., temperatures T2,T1 of FIG. 6). The filter assembly controller 410 is shown as beingconnected to the temperature controller 272 and is in communication withthe filter controller 276. Although certain types of temperature sensorsare shown and described, other types of temperature sensors may beutilized.

FIG. 8 shows an example of a second filter assembly (a core-basedassembly) 450. The second filter assembly 450 may replace any of thesecond filter assemblies of FIGS. 1-5. The second filter assembly 450includes a first low pass filter 452 and a second low pass filter 454.The filters 452, 454 include respective thermocouple cables 456, 458,which are wrapped around corresponding ferrite cores 460, 462 to provideinductances. Although two cores 460, 462 are shown, a common mode chokemay be used, whereby the thermocouple cables are wrapped aroundrespective portions of a single core (e.g., a ring-shaped core). Each ofthe thermocouple cables 456, 458 includes an outer sheath and a pair ofconductors. First ends of conductors in the thermocouple cables 456, 458may be connected to output terminals of a first filter assembly (any ofthe first filter assemblies of FIGS. 1-7). Second ends of the conductorsin the thermocouple cables 456, 458 may be connected to input terminalsof an isolation device (e.g., any of the isolation devices of FIGS.1-6). Capacitances 470, 472 are connected to the sheaths at the outputsof the inductances and to the ground reference 398. The filters 452, 454may supplement the filters of a first filter assembly (e.g., the firstfilter assembly 350 of FIG. 7) and block frequencies above a cut-offfrequency of the filters 452, 454. The cut-off frequency of the filters452, 454 may be the same or different than the cut-off frequency of thelow pass filters of the first filter assembly. The primary purpose ofthe filters 452, 454 is to filter out noise that was coupled to thesignal lines by radiation inside the RF chamber or otherwise picked upafter the first filter assembly.

For further defined structure of the controllers of FIGS. 1-8 see belowprovided method of FIG. 9 and below provided definition for the term“controller”. The systems disclosed herein may be operated usingnumerous methods, an example method is illustrated in FIG. 9. In FIG. 9,a temperature control method of operating a system is shown. Althoughthe following tasks are primarily described with respect to theimplementations of FIG. 9, the tasks may be easily modified to apply toother implementations of the present disclosure. The tasks may beiteratively performed. The tasks may be performed for each station in aplasma chamber.

The method may begin at 500. At 502, a temperature controller (e.g., oneof the temperature controllers 142, 272, 292 of FIGS. 1-5) may determinepredetermined settings for one or more cooling or temperature regulatingdevices (e.g., the fans 190 of FIG. 1, the cooling devices 282 of FIG.4, and/or the valves 298 and the pump 300 of FIG. 5) a current recipeand/or process being performed. The predetermined settings may includepredetermined speeds, frequencies, duty cycles, pressures, valvepositions, etc. to maintain one or more first filter assemblies (FAs)(e.g., any of the first FAs disclosed herein, such as one or more of thefirst FAs 186, 204, 238, 350 of FIGS. 1-5 and 7) at a predeterminedtemperature. The predetermined settings are set to minimize temperaturedifferences across the first FAs between the input terminals and theoutput terminals of the first FAs (e.g., difference between T2 and T1 inFIG. 6 and/or difference between temperatures at (i) terminals 390, 392,and (ii) terminals 394, 396 of FIG. 7). The settings may be set suchthat the temperature differences are at a predetermined value (e.g.,zero) or within a predetermined range of the predetermined value. Thesettings may be based on tabular values relating certain processparameters, process steps, recipe values, etc. to the predeterminedsettings of the cooling and/or temperature regulating devices. Thesettings may be stored in and/or accessed by the temperature controller.

At 504, the temperature controller may operate the one or more coolingor temperature regulating devices at the predetermined settings. At 506,the temperature controller may determine whether closed loop control isbeing performed. If closed loop control is being performed, task 508 isperformed, otherwise task 522 is performed. If closed loop control isnot performed and as a result open loop control is performed, task 504may be performed while tasks 522-534 are performed. If closed loopcontrol is performed, the predetermined settings may be adjusted duringtasks 508-516. Tasks 508-516 may be performed for each of the first FAs.Tasks 522-534 may be performed for each station. Tasks 508-516 may beiteratively and/or continuously performed while tasks 522-532 areperformed.

At 508, the temperature sensors 356, 358 of FIG. 7 or other temperaturesensors may be used to detect temperatures across the first FAs. Thetemperature sensors may generate temperature signals indicative of thetemperatures at the inputs and outputs of the first FAs. The temperaturesignals may be provided to a filter controller (the filter controller294 or the filter assembly controller 410 of FIGS. 5 and 7).

At 510, if (i) the temperatures are not at a predetermined temperature(e.g., 70° C.), (ii) a difference in temperatures across one or more ofthe first FAs is not zero or at the predetermined value, or (iii) adifference in temperatures across one or more of the first FAs isoutside a predetermined range from the predetermined value, then thesettings of the cooling and/or temperature regulating devices may beadjusted accordingly. These adjustments are made based on the detectedtemperatures of the first FA and the predetermined temperature for thefirst FA. This may include zones cooling including adjusting an amountof cooling at an input of a first FA to be different than an amount ofcooling at an output of the first FA or vice versa. For example, a rateand/or a pressure of a gas/cooling fluid provided across the input ofthe first FA or through a cooling block near the input of the first FAmay be different than a rate or pressure of a gas/cooling fluid providedacross the output of the first FA or through the cooling block near theoutput of the first FA. For example, a cooling fluid passing through achannel of a cooling block under the inputs of the first FA may beflowing at a different rate and/or be at a different pressure than acooling fluid being passed through a second channel of the cooling blockunder the outputs of the first FA.

At 512, if the temperature differences are within a predetermined rangeof the predetermined value, task 522 is performed; otherwise task 514may be performed. At 514, a timer may be started. The timer may belocated with the temperature controller. At 516, if a time on the timerhas exceeded a predetermined period or the timer has timed out, task 518may be performed, otherwise task 508 may be performed.

At 518, an alert flag may be set and/or a warning signal may begenerated to indicate that a temperature difference across a first FAhas not been reduced to be at the predetermined value (or zero) orwithin the predetermined range of the predetermined value. Alternativelyor in addition to setting the flag and/or generating the warning signal,another countermeasure may be performed. For example, a processing stepof a wafer may be stopped or prevented from continuing to a next step.Subsequent to task 518, the method may end at 520.

At 522, a thermocouple within a showerhead generates one or moresignals. Tasks 522-532 may be performed for each of the signalsgenerated. For example, as in FIGS. 3-5, if a thermocouple generates afirst signal primarily for solid-state relay control and a second signalfor over current protection, then a first version of tasks 522-532 isperformed for the first signal while a second version of tasks 522-532is also performed for the second signal. The second version may beperformed while the first version is performed.

At 524, the signals generated at 522 are filtered by first filters(e.g., band blocking filters 362, 366) on a PCB of a first FA. At 526,outputs of the first filters are filtered by second filters (e.g., thelow pass filters 364, 368) on the PCB of the first FA. At 528, outputsof the second filters may be filtered by third filters (e.g., 244, 246)of a second FA (e.g., one of the second FAs 188, 206, 244, 246). At 530,outputs of the second filters or the third filters, depending on whetherthe outputs of the second filters are filtered by third filters, areconditioned via an isolation device.

At 532, heating elements and/or cooling of the showerhead are controlledbased on the outputs of the isolation device, as described above. Thismay include (i) controlling an amount of AC current provided tosolid-state relays (e.g., the solid-state relays 250 of FIGS. 3-5),and/or (ii) controlling states of the solid-state relays and amounts ofthe AC current supplied to the heating elements.

At 534, if a processing step of the wafer is complete and/or theprocessing of the wafer is complete, the method may end at 520;otherwise task 502, 506, 508 or 522 may be performed subsequent to task534.

The above-described tasks are meant to be illustrative examples; thetasks may be performed sequentially, synchronously, simultaneously,continuously, during overlapping time periods or in a different orderdepending upon the application. Also, any of the tasks may not beperformed or skipped depending on the implementation and/or sequence ofevents.

FIG. 10 is a plot illustrating station temperatures with traditionalfiltering. A first temperature signal 600 for a first electrode of afirst station, a second temperature signal 602 for a second electrode ofa second station, and an RF status signal 604 are shown. The secondtemperature signal 602 overlaps the first temperature signal 600 exceptduring certain periods of time along a performed process, where thesecond temperature signal 602 is higher or lower than the firsttemperature signal 600. The temperature signals 600, 602 are providedusing traditional filtering, which includes core-based low pass filters,similar to the low pass filters shown in FIG. 8. The RF status signal604 indicates when RF voltages are supplied to the electrodes.

Insulation of the second electrode (or showerhead) associated with thesecond temperature signal 602 has degraded, such that inaccurate DCvoltage signals are being detected by a thermocouple of the secondelectrode. For this reason and although the second electrode isexperiencing the same cooling or temperature regulation as the firstelectrode, the second temperature signal deviates from the firsttemperature signal, as shown.

FIG. 11 is a plot illustrating station temperatures with filtering asdisclosed herein. By filtering signals received from thermocouples asdescribed above with respect to FIGS. 1-9, DC voltage signals of anon-insulation degraded electrode and an insulation degraded electrodematch after filtering. This filtering includes the filtering performedby the first FAs. This is shown by temperature signals 600, 602 of FIG.10. The temperature signals 610, 612 are for the same electrodes as thetemperature signals 600, 602 of FIG. 10. A RF status signal 614 is alsoshown.

The above disclosed examples include RF filtering via PCBAs and signalconditioners of thermocouple signals received from a showerhead. Thisfilters out RF energy that has coupled to thermocouple lines andisolates DC signals perturbing temperature measurements and closed looptemperature control of a showerhead. The RF filtering isolates RF energyto corresponding stations. The PCBAs are temperature controlled andaddress temperature offsets, which can occur when voltages from athermocouple (small DC voltages) transfer across conductors. Isolationdevices are provided to isolate DC signals generated by sources otherthan thermocouples from temperature controllers. The isolation devicesmay isolate the temperature controllers from a chassis ground.

Further, various embodiments are disclosed herein. Although each of theembodiments are described as having certain features, any one or more ofthe features described with respect to any one embodiment of thedisclosure can be implemented in and/or combined with features of any ofthe other embodiments, even if that combination is not explicitlydescribed. In other words, the described embodiments are not mutuallyexclusive, and permutations of one or more embodiments with one anotherremain within the scope of this disclosure.

Spatial and functional relationships between elements (for example,between modules, circuit elements, semiconductor layers, etc.) aredescribed using various terms, including “connected,” “engaged,”“coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and“disposed.” Unless explicitly described as being “direct,” when arelationship between first and second elements is described in the abovedisclosure, that relationship can be a direct relationship where noother intervening elements are present between the first and secondelements, but can also be an indirect relationship where one or moreintervening elements are present (either spatially or functionally)between the first and second elements. When a first element is adjacentto a second element, the first element may be in contact with the secondelement or the first element may be spaced away from the second elementwithout any intervening element between the first element and the secondelement. When a first element is between a second element and a thirdelement, the first element may be directly connected to the secondelement and the third element (referred to as “directly between”) orintervening elements may be connected (i) between the first element andthe second element, and/or (ii) between the first element and the thirdelement. As used herein, the phrase at least one of A, B, and C shouldbe construed to mean a logical (A OR B OR C), using a non-exclusivelogical OR, and should not be construed to mean “at least one of A, atleast one of B, and at least one of C.”

In some implementations, a controller is part of a system, which may bepart of the above-described examples. Such systems can includesemiconductor processing equipment, including a processing tool ortools, chamber or chambers, a platform or platforms for processing,and/or specific processing components (a wafer pedestal, a gas flowsystem, etc.). These systems may be integrated with electronics forcontrolling their operation before, during, and after processing of asemiconductor wafer or substrate. The electronics may be referred to asthe “controller,” which may control various components or subparts ofthe system or systems. The controller, depending on the processingrequirements and/or the type of system, may be programmed to control anyof the processes disclosed herein, including the delivery of processinggases, temperature settings (e.g., heating and/or cooling), pressuresettings, vacuum settings, power settings, radio frequency (RF)generator settings, RF matching circuit settings, frequency settings,flow rate settings, fluid delivery settings, positional and operationsettings, wafer transfers into and out of a tool and other transfertools and/or load locks connected to or interfaced with a specificsystem.

Broadly speaking, the controller may be defined as electronics havingvarious integrated circuits, logic, memory, and/or software that receiveinstructions, issue instructions, control operation, enable cleaningoperations, enable endpoint measurements, and the like. The integratedcircuits may include chips in the form of firmware that store programinstructions, digital signal processors (DSPs), chips defined asapplication specific integrated circuits (ASICs), and/or one or moremicroprocessors, or microcontrollers that execute program instructions(e.g., software). Program instructions may be instructions communicatedto the controller in the form of various individual settings (or programfiles), defining operational parameters for carrying out a particularprocess on or for a semiconductor wafer or to a system. The operationalparameters may, in some embodiments, be part of a recipe defined byprocess engineers to accomplish one or more processing steps during thefabrication of one or more layers, materials, metals, oxides, silicon,silicon dioxide, surfaces, circuits, and/or dies of a wafer.

The controller, in some implementations, may be a part of or coupled toa computer that is integrated with the system, coupled to the system,otherwise networked to the system, or a combination thereof. Forexample, the controller may be in the “cloud” or all or a part of a fabhost computer system, which can allow for remote access of the waferprocessing. The computer may enable remote access to the system tomonitor current progress of fabrication operations, examine a history ofpast fabrication operations, examine trends or performance metrics froma plurality of fabrication operations, to change parameters of currentprocessing, to set processing steps to follow a current processing, orto start a new process. In some examples, a remote computer (e.g. aserver) can provide process recipes to a system over a network, whichmay include a local network or the Internet. The remote computer mayinclude a user interface that enables entry or programming of parametersand/or settings, which are then communicated to the system from theremote computer. In some examples, the controller receives instructionsin the form of data, which specify parameters for each of the processingsteps to be performed during one or more operations. It should beunderstood that the parameters may be specific to the type of process tobe performed and the type of tool that the controller is configured tointerface with or control. Thus as described above, the controller maybe distributed, such as by including one or more discrete controllersthat are networked together and working towards a common purpose, suchas the processes and controls described herein. An example of adistributed controller for such purposes would be one or more integratedcircuits on a chamber in communication with one or more integratedcircuits located remotely (such as at the platform level or as part of aremote computer) that combine to control a process on the chamber.

Without limitation, example systems may include a plasma etch chamber ormodule, a deposition chamber or module, a spin-rinse chamber or module,a metal plating chamber or module, a clean chamber or module, a beveledge etch chamber or module, a physical vapor deposition (PVD) chamberor module, a chemical vapor deposition (CVD) chamber or module, anatomic layer deposition (ALD) chamber or module, an atomic layer etch(ALE) chamber or module, an ion implantation chamber or module, a trackchamber or module, and any other semiconductor processing systems thatmay be associated or used in the fabrication and/or manufacturing ofsemiconductor wafers.

As noted above, depending on the process step or steps to be performedby the tool, the controller might communicate with one or more of othertool circuits or modules, other tool components, cluster tools, othertool interfaces, adjacent tools, neighboring tools, tools locatedthroughout a factory, a main computer, another controller, or tools usedin material transport that bring containers of wafers to and from toollocations and/or load ports in a semiconductor manufacturing factory.

None of the elements recited in the claims are intended to be ameans-plus-function element within the meaning of 35 U.S.C. § 112(f)unless an element is expressly recited using the phrase “means for,” orin the case of a method claim using the phrases “operation for” or “stepfor.”

What is claimed is:
 1. A method comprising: receiving a first signalfrom a first sensor at a first filter; preventing passage of a firstportion of the first signal via the first filter, wherein the firstportion of the first signal is at a first radio frequency, and wherein asecond portion of the first signal is indicative of a first temperatureof a first electrode in a plasma chamber; outputting a second signalfrom the first filter; receiving the second signal at a second filter;preventing passage of a portion of the second signal via the secondfilter, wherein the portion of the second signal is at a second radiofrequency, wherein the second radio frequency is less than the firstradio frequency, and wherein the first filter and the second filter areimplemented on a printed circuit board; and adjusting a temperature ofthe first electrode based on an output of the second filter.
 2. Themethod of claim 1, wherein: the first filter is a band stop filter andpermits passage of the portion of the second signal; and the secondfilter is a low pass filter.
 3. The method of claim 1, furthercomprising controlling operation of a cooling device to maintain atemperature of a filter assembly at a predetermined temperature, whereinthe filter assembly comprises the first filter and the second filter. 4.The method of claim 3, wherein the cooling device is a fan.
 5. Themethod of claim 3, wherein the cooling device is a valve or a pump. 6.The method of claim 3, further comprising controlling flow of a fluidthrough a block thermally connected to a first filter assembly tomaintain the temperature of the first filter assembly at thepredetermined temperature, wherein the filter assembly comprises thefirst filter and the second filter.
 7. The method of claim 1, furthercomprising controlling operation of one or more temperature adjustingdevices to maintain a temperature of a filter assembly at apredetermined temperature, wherein the filter assembly comprises thefirst filter and the second filter.
 8. The method of claim 7, furthercomprising: generating a third signal via a second sensor, wherein thethird signal is indicative of a temperature at an input of the filterassembly; generating a fourth signal via a third sensor, wherein thefourth signal is indicative of a temperature at an output of the filterassembly; and controlling a cooling device based on the third signal andthe fourth signal.
 9. The method of claim 1, further comprising:receiving the output of the second filter at a third filter; andadjusting the temperature of the first electrode based on an output ofthe third filter, wherein the third filter includes thermocouple lineswrapped around a core.
 10. The method of claim 1, further comprising:filtering an output of the second filter via a third filter; generatingan output via a fourth filter based on the second signal received fromthe first sensor; receiving an alternating current based on the outputof the fourth filter; and adjusting a temperature of the first electrodebased on an output of the third filter.
 11. The method of claim 1,further comprising: receiving a first radio frequency signal and asecond radio frequency signal at the first electrode, wherein the firstradio frequency signal is at the first radio frequency, the second radiofrequency signal is at the second radio frequency, and the second radiofrequency is less than the first radio frequency; preventing passage ofthe first radio frequency and permitting passage of the second radiofrequency via the first filter; and preventing passage of the secondradio frequency via the second filter.
 12. The method of claim 11,further comprising prevents passage of signals at frequencies above acut-off frequency including the first radio frequency via the secondfilter.
 13. The method of claim 1, further comprising adjusting thetemperature of the first electrode by adjusting an amount of currentsupplied to the first electrode.
 14. The method of claim 1, furthercomprising: adjusting the temperature of the first electrode byadjusting an amount of current supplied to one or more of a plurality ofrelays; and receiving current from the plurality of relays at the firstelectrode.
 15. The method of claim 1, further comprising receiving thesecond signal from the first filter at the second filter.
 16. The methodof claim 1, wherein the first sensor is a thermocouple.
 17. The methodof claim 1, further comprising controlling heating elements and/orcooling of a showerhead based on the output of the second filter.